1. Field of the Invention
The present invention relates in general to a hydraulic pressure control apparatus or hydraulic braking apparatus of a motor vehicle, which is capable of controlling a pressure in a wheel brake cylinder of a hydraulically operated brake for braking a wheel of the vehicle. In particular, the present invention relates to such an apparatus which includes a device for estimating an amount of fluid stored in a reservoir to which the fluid is discharged to reduce the pressure in the brake cylinder.
2. Discussion of the Related Art
An example of a hydraulically operated braking apparatus of the type indicated above is disclosed in JP-A1-119462. This braking apparatus includes a hydraulic pressure control apparatus for a brake including a brake cylinder activated by a pressurized fluid for braking a wheel of a vehicle, a reservoir for storing the fluid discharged from the brake cylinder, and a pump for pumping up the fluid from the reservoir, and the control apparatus includes (a) a pressure control device which discharges the fluid from the brake cylinder, into the reservoir, to reduce a pressure of the fluid in the brake cylinder, and supplies the fluid pumped up from the reservoir, to the brake cylinder, to increase the pressure of the fluid in the brake cylinder; and (b) reservoir fluid amount estimating means for estimating a cumulative amount of flow of the fluid from the brake cylinder into the reservoir and a cumulative amount of flow of the fluid out of the reservoir, and estimating an amount of the fluid stored in the reservoir on the basis of the estimated cumulative amount of flow of the fluid into the reservoir and the estimated cumulative amount of flow of the fluid out of the reservoir.
In the prior control apparatus, the reservoir fluid amount estimating means estimates the cumulative amount of flow of the fluid into the reservoir based on a pressure reducing time during which the pressure in the brake cylinder is reduced by the pressure control device, and estimates the cumulative amount of flow of the fluid out of the reservoir based on a pumping-up time during which the fluid is pumped up from the reservoir by the pump.
Once the reservoir fluid amount estimating means starts its operation, it continues to estimate the amount of the fluid stored in the reservoir (hereinafter referred to as the "reservoir fluid amount") until a continuous pressure control operation is finished by the pressure control device. However, as the estimating operation continues, the estimated reservoir fluid amount may largely deviate from the actual reservoir fluid amount. In this case, the estimating operation should be stopped. In addition, there are some cases where it is desirable not to continue the estimation though the estimated reservoir fluid amount value is not different from the actual value. For example, in the case where the prior control apparatus includes a control means for performing a predetermined control operation when the estimated reservoir fluid amount value coincides with a predetermined value, there are some cases where it is desirable to operate the control means compulsorily by changing the current estimated reservoir fluid amount value to the predetermined value.